X-Ray Fluorescence and Natural History

X-Ray Fluorescence and Natural History

How XRF Helps XRF can be used both quantitatively (homogenous samples) and quantitatively (heterogenous samples).! Trace elements in a fossil can help identify source, or give insight into diagenetic processes Chemostratigraphic profiles can help understand formation processes and paleoenvironments In curation contexts, elemental data can help with conservation decisions (specifically regarding arsenic, uranium, lead, etc.)!2

How we see color Color is fundamentally a fluorescence process: a photon is emitted from a source The emitted photon interacts with the molecules in the sample Based on the properties of the molecule, the photon is either reflected back, scattered, or absorbed. Our eyes see the reflected photon through our cone cells and send the information to a processor (our minds) which perceive color.! Red is 1 ev Violet is 3 ev Photon # Red 1 ev 3 ev

How it Works What is x-ray fluorescence? In the most basic terms, x-ray fluorescence is the process in which: a photon is emitted from an x-ray source The emitted photon interacts with the atoms in the sample In some cases, this interaction causes an electron to get knocked out of the inner shell of a given atom When an electron leaves an inner shell, the atom becomes unstable and wants to fill the vacancy, so an electron from a higher shell drops down to fill that vacancy When an electron drops from a higher to a lower shell, a certain energy is released in the form of another photon, which is characteristic not only to each element, but to each shell transition; this is fluorescence In x-ray fluorescence instruments, a detector is used to pick up the characteristic fluorescent energies.!!

M L K

M L K

M L K

M L K

M L K

Kα1 M L K

Kβ1 M L K

# of Photons/Light Intensity Analysis of Spectra The x axis shows increasing energy - each element lights up at a different and unique energy

How deep can we measure? Silicates I I0 = e(-µ/ρ)x Silicate (Glass, Ceramic, Obsidian, Pyrex) 4 Penetration Depth (cm) 3 2 1 0 0 10 20 30 40 kev As you go up in energy, you analyze deeper within the artifact

How deep can we measure? Ceramics Element Photon Emitted energy (kev) Analysis depth in Ceramic(cm) O 0.53 0.000001 Na 1.04 0.0007 Mg 1.2 0.00096 Al 1.47 0.0017 Si 1.74 0.0027 P 2.01 0.0013 Ca 3.69 0.0064 Cr 5.41 0.0192 Fe 6.4 0.03 Cu 8.01 0.058 Zn 8.64 0.077 Pb 10.55 0.113 Zr 15.78 0.384

The 5 Parameters for Data Collection 1. The same energy (in kev) 2. The same current (in µa) 3. The same filter 4. The same time of analysis 5. The same atmosphere (air, vacuum, etc.)

Imaging with XRF XRF can be used to create elemental images! A simple color ramp can be used to show high and low concentrations of elements False-color images can be generated when red, green, or blue is assigned to different elements!16

Fossil Fish from Green River Formation Strontium Kα1 (14.16 kev) y 2.5 2.0 1.5 1.0 0.5 0.0 Net Photons z 50000 40000 30000 20000 10000 10 10 0 1 2 3 4 x

Fossil Fish from Green River Formation Strontium, Silica, and Phosphorous Kα1 2.5 Net Photons (mm) y 2.0 1.5 1.0 Strontium Silica Phosphorous 0.5 0.0 0 1 2 3 4 x (mm)

Fossil Fish from Green River Formation Strontium, Silica, and Phosphorous Kα1 2.5 (mm) y 2.0 1.5 1.0 Net Photons Zirconium Potassium Phosphorous 0.5 0.0 0 1 2 3 4 x (mm)

When to quantify results? 4000 y = 0.0163x - 71.068 R² = 0.9768 Zirconium (parts per million) 3000 2000 1000 0 0 45000 90000 135000 180000 Zirconium (gross photons)

When to quantify results? Quantification is a set of linear models/regressions Lucas-Tooth and Price (1961) Equation: Ci = r0 + Ii[ri + Σ(rinIn)]! In which Ci represents the concentrate of a given element of the sample in weight % or ppm, r0 is the intercept/constant, ri is the slope of photons for element i, rin is the slope of photons for element n that influence the fluorescence of element i, Ii is the quantity of photons for element i, and In is the quantity of photons for element n.

When to quantify results? Quantification is basically a complicated set of linear models/regressions

0.0600 Molybedinum (Mo) Peso % 0.0450 0.0300 0.0150 0.0000 11210.0t 11211.1t 11214.0t 11215.0t 11218.0t 11221.0t 11224.0t 11226.0t 11229.0t 11232.0t 11235.0t 11238.3t 11240.0t 11243.0t 11246.0t 11249.0t 11252.0t 11256.0t 11258.3t 11261.0t 11264.0t 11267.0t 11270.0t 11273.0t Profundidad 40.0000 Calcium (Ca) Peso % 30.0000 20.0000 10.0000 0.0000 11210.0t 11211.1t 11214.0t 11215.0t 11218.0t 11221.0t 11224.0t 11226.0t 11229.0t 11232.0t 11235.0t 11238.3t 11240.0t 11243.0t 11246.0t 11249.0t 11252.0t 11256.0t 11258.3t 11261.0t 11264.0t 11267.0t 11270.0t 11273.0t!23 Profundidad

Quantitative and Qualitative XRF XRF can be used both quantitatively and qualitatively! While quantitative data can be collected from homogenous materials, qualitative data from heterogenous materials can be helpful as well!24

Picture from area scanned

x 1E3 Pulses Ca 100 Spectra at various locations at various scales 80 60 40 20 0 6 Si x 1E3 Pulses S Cl K Ti Cr Mn 2 4 6 8 - kev - Cl Ca Fe Fe Note the coherent (Bragg) Zn scattering occurring when the beam strikes various crystals at various orientations in the rock Note the beam size is 0.065mm 4 2 K Si S Ti Cr Mn Zn 0 2 4 6 8 - kev -

5 4 x 1E3 Pulses Note the coherent (Bragg) scattering occurring when the beam strikes various crystals at various orientations in the rock. Note the beam size is 0.065mm 3 Cl Ar 2 1 0 2.40 2.60 2.80 3.00 - kev -

x 1E3 Pulses 2.5 2.0 Note the coherent (Bragg) scattering occurring when the beam strikes various crystals at various orientations in the rock. Note the beam size is 0.065mm 1.5 Cr Mn Fe Zn 1.0 0.5 0.0 6 8 10 - kev -